1. Field of the Invention
The present invention relates to an image pickup apparatus with an AF sensor unit, and more particularly, to an image pickup apparatus with a man body having an AF sensor unit fixed thereto promptly with high precision by a parallax adjustment method.
2. Description of the Related Art
There has been developed an image pickup apparatus that has an AF sensor unit outside its image pickup optical system and is designed to measure the distance from a subject with the use of the AF sensor unit.
The AF sensor unit used in this manner may employ a passive AF method of performing measurement based on a triangular ranging principle, using two sets of optical systems each including a lens and a distance measuring image pickup element, for example.
Such an AF sensor unit needs to be fixed to an image pickup apparatus while being tilted at a predetermined angle in the optical axis direction of the image pickup lens such that the orientations of the two sets of optical systems correspond to the center of a subject image formed by picking up an image of the center of the subject located at a specific distance. Therefore, an AF sensor unit is normally mounted on the main body of an image pickup apparatus by performing a positioning and securing process with high precision, or by a so-called parallax adjustment method (see Japanese Laid-Open Patent Publication (Kokai) No. 2001-208536, for example).
A description will now be made of a method of mounting a conventional AF sensor unit on the main body of an image pickup apparatus by implementing a parallax adjustment method through an example case where an AF sensor unit of a passive AF type is fixed to a video camera, with reference to FIGS. 4 and 5.
In FIGS. 4 and 5, an AF sensor unit 1001 has built-in two sets of a lens and an AF sensor (AF-service image pickup elements). This AF sensor unit 1001 has a flexible board 1009 extending from the main body of the AF sensor unit 1001 for transmitting electric signals from the built-in AF sensor to a predetermined electric circuit (FIG. 5).
A lens unit 1004 of the video camera has an AF sensor holder-mounting unit 1002 for retaining the AF sensor unit 1001 in a holding manner screwed thereto with an AF sensor holder-mounting unit-fixing screw 1003.
This AF sensor unit 1001 has two adjustment holes 1010 therein. The AF sensor holder-mounting unit 1002 has a stopper boss 1008 protruding from a bottom portion thereof. The stopper boss 1008 is configured to be fitted into a concave portion (not shown) formed in the bottom portion of the AF sensor unit 1001, and serve as a stopper part when the attitude of the AF sensor unit 1001 is adjusted.
This AF sensor unit 1001 is to be subjected to a parallax adjustment method, described later, of performing the movement in adjustment directions (X, Y) 1007 with the use of adjustment tool pins 1005, each of which has a tapered end portion, protruding from a special-purpose adjustment tool. The AF sensor unit 1001 subjected to the parallax adjustment method is bonded and fixed to the AF sensor holder-mounting unit 1002 with a UV curing adhesive agent 1006 (at two spots).
A description will now be made of the parallax adjustment method for the AF sensor unit 1001.
According to this parallax adjustment method, the AF sensor unit 1001 is first placed on the AF sensor holder-mounting unit 1002. On this occasion, into the concave portion (not shown) formed on the bottom portion of the AF sensor unit 1001 is inserted the stopper boss 1008 of the AF sensor holder-mounting unit 1002, which enables the AF sensor unit 1001 to be supported by a pivot bearing and is set in a position-variable state.
In this state, the adjustment tool pins 1005, each of which has the tapered end portion, protruding from the special-purpose adjustment tool are inserted into the two adjustment holes 1010, which allows a predetermined downward load to be applied to the AF sensor unit 1001.
The adjustment tool pins 1005 are configured to pivotally move in the adjustment directions (X, Y) 1007 when a predetermined tab of the special-purpose adjustment tool (not shown) is rotatably moved. This operation enables the AF sensor unit 1001 to be pivotally moved about the stopper boss 1008 with its position adjusted.
Moreover, as a method of measuring the fixed angle with respect to the optical axis direction of the image pickup lens of the AF sensor unit 1001, there is normally used an output waveform measurement method of measuring the waveform of the AF sensor output projected on the chart with a chart placed at a predetermined distance from the image pickup lens.
After the AF sensor unit 1001 has thus been positioned at a predetermined fixed angle with the use of the special-purpose adjustment tool, a UV curing adhesive agent 1006 is applied to the two spots shown in the drawing, and then the UV curing adhesive agent 1006 is cured by UV rays emitted onto the UV curing adhesive agent 1006 for a certain period of time, before the adjustment tool pins 1005 are pulled out.
As described above, the AF sensor unit 1001 is positioned and fixed to the AF sensor holder-mounting unit 1002 of the lens unit 1004 in a desired position.
By the above parallax adjustment method, however, the AF sensor unit 1001 together with the AF sensor holder-mounting unit 1002 unfavorably bends downward when the adjustment tool pins 1005 are inserted into the two adjustment holes 1010 with the predetermined downward load applied to the AF sensor unit 1001.
Therefore, when the load of the adjustment tool pins 1005 is removed after the parallax adjustment (after the adjustment tool pins 1005 have been pulled out), the AF sensor holder-mounting unit 1002 and the like are elastically returned, thereby causing the AF sensor unit 1001 to move from the position determined by the parallax adjustment method, which provides an error. Also, the error caused by the movement from the position determined by the parallax adjustment makes it difficult to mount the AF sensor unit 1001 on the main body of the image pickup apparatus with high precision.
Also, the AF sensor unit 1001 is fixed at two spots with the UV curing adhesive agent 1006 after the parallax adjustment; accordingly, the AF sensor unit 1001 is affected by the adhesive curing stress, temperature changes, drops, and vibrations, thereby providing a deviation in the fixed position of the AF sensor unit 1001. This makes it difficult to position and secure the AF sensor unit 1001 with high precision.
Further, the time consumed by processes of the parallax adjustment method disadvantageously becomes longer, because of the adhesion curing time for the UV curing adhesive agent 1006.